(1) Field of the Invention
The present invention relates to a web offset printing press, particularly, to a blanket washing method, and a blanket washing solution removing method after washing for use in a web offset printing press of a shaftless type.
(2) Description of Related Art
In a web offset printing press, a pattern is once transferred from a machine plate of a plate cylinder onto a blanket mounted on the outer peripheral surface of a blanket cylinder, then printed on a web from the blanket. Continuous printing allows residue of ink to attach to the blanket. When the quantity of the residual ink increases, this adversely affects on the printing quality of products. For this, when a certain number of sheets are printed, the printing is once stopped, the blanket cylinder is thrown off to wash the blanket (hereinafter referred as blanket wash). When the plate is changed and the printing is resumed with a new plate, it is necessary to remove a pattern of the old plate from the blanket. When the plate is changed, blanket wash is carried out, as well. Blanket wash is generally performed by rotating the blanket cylinder while it is thrown off and supplying a washing solution to the blanket.
A web offset printing press generally comprises, as shown in FIG. 17, a feeding unit 2 having a web roll 1, an infeed unit 3 drawing out a web (strip-like paper) from the web roll 1, printing units 4 including a plurality of printing units 4a through 4d each having the above plate cylinder, the blanket cylinder, etc., a drier unit 5 applying heat onto the web 10, on which printing has been performed, to dry it, a cooling unit 6 cooling the heated web 10, a web pass unit 7, and a folder 8 processing the strip-like web 10 into signatures, as essential parts. Heretofore, a web offset printing press of a line-shaft type (shaft machine) is general, in which driving units of the infeed unit 3, the printing units 4a through 4d, the cooling unit 6, the web pass unit 7 and the folder 8, etc. are connected to a main motor 11 through a common line shaft 12, and the driving units are integrally driven under a driving control on the main motor 11 by a control unit 15.
In such a shaft machine, the printing units 4a through 4d are connected to the infeed unit 3 making the web 10 run and the cooling unit 6 by the line shaft 12, so that the printing units 4a through 4b rotate at a speed equal to the running speed of the web 10. When blanket wash is carried out, the web 10 runs at a speed equal to the peripheral speed of the blanket cylinder. During which, the web 10 becomes all spoiled, because no printing is, of course, carried out.
Heretofore, before printing is started, the printing press is driven at a slow-operating speed (preferably the minimum speed) to decrease the run length of the web 10, thereby suppressing generation of spoilage. When blanket wash is carried out during printing, the current printing speed is reduced to a certain extent, and blanket wash is carried out. After completion of the washing, the speed is again increased to the printing speed, and the printing is resumed. Whereby, the run length of the web 10 during the blanket wash is decreased, thereby suppressing generation of spoilage.
Recently developed was a web offset printing press (shaftless machine) of a shaftless type (separately driving type) without a conventional line shaft, in which, as shown in FIG. 18, drive motors 24a through 24d, 23, 26, 27 and 28 are provided to respective driving units such as printing units 4a through 4d, an infeed unit 3, a cooling unit 6, a web pass unit 7, a folder 8, etc. In this shaftless machine, control units 34a through 34d, 33, 36, 37 and 38 are provided correspondingly to the respective drive motors 24a through 24d, 23, 26, 27 and 28. The drive motors 24a through 24d, 23, 26, 27 and 28 are electrically synchronized and operated under synchronous controls of the control units 34a through 34d, 33, 36, 37 and 38.
Also developed was a web offset printing press of another type, in which only printing units 4a through 4d are connected by a line shaft 22 and integrally driven by a drive motor 24 through the line shaft 22, and drive motors 23, 26, 27 and 28 are respectively provided to another driving units such as an infeed unit 3, a cooling unit 6, a web pass unit 7, a folder 8, etc., as shown in FIG. 19. In a web offset press of this type, control units 33, 34, 36, 37 and 38 are provided correspondingly to the respective drive motors 23, 24, 26, 27 and 28, and the drive motors 23, 24, 26, 27 and 28 are electrically synchronized and operated under synchronous controls of the control units 33, 34, 36, 37 and 38. Since web offset printing presses of this type are basically of a shaftless type although having a line shaft in part, the web offset printing presses show in FIGS. 18 and 19 will be generally referred as shaftless machines, hereinafter. Blanket wash can be carried out in the known manner as above in these shaftless machines, as a matter of course. Actually, blanket wash is carried out in the shaftless machines just as done in shaft machines.
However, it is necessary in the known manner to decrease the peripheral speed of the blanket cylinder synchronized with the running speed of the web 10, that is, the washing speed during the blanket wash, in order to decrease the run length of the web 10. This causes degradation of the effect of washing, or causes a longer washing time, resulting in an increase in run length of the web 10, and an increase in amount of spoilage. For this, there are requirements for more effective blanket wash, and for improvement in the productivity by decreasing the amount of spoilage generated at the time of blanket wash as much as possible. Particularly, shaftless machines have characteristics that the printing units can be driven independently of other driving units, so that it is desired to solve the above problems while making the best use of the characteristics of the shaftless machines.
A gap is generally formed in the blanket cylinder to catch a blanket therein, whereby the blanket is wound around the blanket cylinder. However, the washing solution enters in the gap at the time of blanket wash. The washing solution in the gap flies out by centrifugal force according to the peripheral speed of the blanket cylinder. When the operation is resumed, the web is contaminated by the washing solution flying out from the gap of the blanket cylinder for a while after the web has reached the printing speed. Printed matter printed during this has a high probability that contamination by the washing solution is attached thereon, thus being generally treated as spoilage from the viewpoint of the printing quality. This is also a common problem among the known shaft machines and shaftless machines. There is thus a demand to decrease the amount of spoilage caused by the washing solution after the blanket wash to improve the productivity.